Liquid phase etching method and liquid phase etching apparatus

ABSTRACT

A liquid phase etching method which comprises spraying a chemically reactive liquid, with a specific speed, to a solid article, an aggregate of solid articles or a gelatinous material to be treated; and a liquid etching apparatus having a mechanism for holding a processing object to be treated and a nozzle structure for spraying a chemically reactive liquid to the processing object to be treated which is held by the mechanism. The method and apparatus allow the significant improvement of the etching rate while maintaining the accuracy of etching.

This application is a divisional of U.S. patent application Ser. No.10/546,015, filed Aug. 18, 2005, which is a National Phase ofPCT/JP2004/002073, filed on Feb. 23, 2004, all of which are incorporatedherein by reference.

TECHNICAL FIELD

The present invention relates to a technical field of processing thesurface of solid materials or other processing objects, in particular afield of forming fine pattern on them. The field includes, for example,a liquid phase etching method and a liquid phase etching apparatus foruse in manufacture of semiconductor device or MEMS(micro-electro-mechanical system) device.

BACKGROUND ART

In processing (etching) process of semiconductor as a typical example offine patterning, the semiconductor surface is irradiated with reactivegas in plasma state, and the semiconductor is processed into desiredshape.

Explaining briefly by referring to FIG. 9, a vacuum chamber 1 is coupledto a vacuum pump 2 for creating vacuum. A processing object like siliconwafer 3 is placed in the vacuum chamber 1, and desired gas isintroduced, and plasma 4 is generated to cause interaction with thesurface of the processing object, and the processing object isprocessed. In FIG. 9, the processing object is etched.

Meanwhile, as disclosed in Japanese Patent Unexamined Publication No.H9-27654, the conventional etching was often processed by immersing thesolid processing object in liquid. However, etching in the liquid issufficiently fast in etching processing speed, but is not suited to finepatterning because etching tends to be isotropic.

The reason of using plasma in etching is to make etching anisotropic inorder to meet the demand for higher precision in fine patterning.

However, when plasma is used in etching, the processing speed issacrificed. As a result, in the semiconductor industrial field,typically, it took about 10 minutes to process one wafer.

DISCLOSURE OF THE INVENTION

The etching method of the invention is etching a processing object whichmay be either solid, solid assembly or gel material, by spraying achemically reactive liquid at a specified speed.

Also, the etching method of the invention is spraying a chemicallyreactive liquid to a processing object placed in a vacuum chamber, byusing a nozzle mechanism. The degree of vacuum in the vacuum chamberwhile processing the processing object may be a sufficient degree ofvacuum for preventing generation of impulse wave when surpassing thesonic speed at the time of jet injection of liquid.

Also, the etching method of the invention is further characterized byimpinging the liquid particles charged on the surface to the processingobject, which is either solid, solid assembly or gel material, withinduced acceleration and induced deceleration in electric field ormagnetic field, by applying an electric charge to injected liquidparticles.

Also, the etching method of the invention is further characterized byprocessing the solid or solid assembly selectively by sprayingchemically reactive liquid to the portion exposed from the mask, bycovering part of the surface of solid or solid assembly with a resinmaterial and using as mask.

Also, the etching apparatus of the invention is comprising a mechanismfor holding a processing object and a nozzle structure for sprayingchemically reactive liquid to the held processing object.

By using the liquid phase etching method and liquid phase etchingapparatus of the invention, the etching speed can be enhancedsubstantially.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional view of liquid phase etching apparatusin an embodiment of the invention.

FIGS. 2A to 2D are process charts showing other processing process inthe embodiment of the invention.

FIGS. 3A to 3C are process charts showing other processing process inthe embodiment of the invention.

FIG. 4 is a schematic sectional view of liquid phase etching apparatusin the embodiment of the invention.

FIG. 5 is a schematic sectional view of another liquid phase etchingapparatus in the embodiment of the invention.

FIG. 6 is a schematic sectional view of another liquid phase etchingapparatus in the embodiment of the invention.

FIG. 7 is a schematic sectional view of a different liquid phase etchingapparatus in the embodiment of the invention.

FIG. 8 is a schematic sectional view of a further liquid phase etchingapparatus in the embodiment of the invention.

FIG. 9 is a schematic sectional view of plasma etching apparatus in aprior art.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention is intended to realize both characteristics of (1) highspeed etching by using liquid and (2) anisotropic etching by usingplasma, simultaneously by spraying liquid to the processing object at anextremely high speed, and hence presents a processing technology capableof processing at high speed and having an extremely sharp anisotropy.

The system capable of impinging liquid drops at super high speed alsohas an effect of generating plasma on the top surface of the processingobject when the liquid drops impinge, so that the features of theinvention may be exhibited more outstandingly.

The invention enables to transfer the existing “etching process” usingplasma to processing in liquid, which is high in processing capability,and hence the productivity is improved from several times to one digithigher. The semiconductor industry requires a tremendous investment formanufacturing equipment. It is extremely difficult to realize the chipunit price worthy of investment, and it is very difficult to adapt toso-called silicon cycle. Therefore, if the etching process time can beimproved by one digit, the productivity is enhanced and it is expectedto change the industrial structure dramatically.

A preferred embodiment of the invention is described below whilereferring to the accompanying drawings. In the drawings, the componentshaving same basic function are identified with same reference numerals.

Preferred Embodiment

A preferred embodiment of the invention is explained by referring toembodiment 1. FIG. 1 is an explanatory diagram of liquid phase etchingapparatus used in the preferred embodiment. Referring now to FIG. 1, theoutline of the etching apparatus of embodiment 1 is explained. A vacuumchamber 10 is coupled to a vacuum pump 20 for creating vacuum. A stage40 and plural nozzles 50 are placed in the vacuum chamber 10. The stage40 holds a processing object 30 which is either solid, solid assembly orgel material. The nozzles 50 are connected to a liquid feed device 60for feeding specified liquid, and particles of chemically reactiveliquid 70 can be sprayed to the processing object 30. From a variety ofliquid 70 capable of etching the processing object 30, a solvent suitedto the processing object is selected and used.

Keeping the vacuum chamber at a higher degree of vacuum than about 1E-3Torr (that is, at lower pressure), the liquid 70 is sprayed from thenozzles 50 at a speed of over 1000 km/hour. The sprayed liquid 70 wetsthe processing object surface 31, which is etched simultaneously.

If wettability of liquid 70 on the processing object surface 31 is poor,a surface active agent is sprayed to the processing object surface froma spray outlet 81 of a surface active agent feed device 80. The surfaceactive agent may be sprayed before spraying of liquid 70, simultaneouslywith spraying, or right after spraying of liquid 70. By the presence ofsurface active agent, the liquid 70 permeates into all parts of theprocessing object surface 31, and it is etched uniformly.

For example, when the liquid 70 is sprayed to the processing object 30by accelerating to a speed of more than 10,000 km/hour, part of liquidcomponents may be transformed into plasma by gaining a high energy. Thegenerated plasma is effective to activate the processing object surface31, and further accelerate the etching process speed.

Anticorrosive processing of nozzles 50 is explained.

Nozzles are not always made of materials excellent in corrosionresistance. If nozzles are made of materials not so high in corrosionresistance, the nozzle basic shape is formed by using a material suitedto nozzle processing, and the surface directly contacting with theetching liquid must be coated with an anticorrosive substance. Thiscoating process is either irradiation of nozzle surface directly withplasma mainly composed of desired anticorrosive substance, orirradiation of nozzle surface with plasma for generating ananticorrosive substance by reacting with the material forming the basicshape. Coating the nozzle surface with an anticorrosive substanceenables the corrosion resistance of the nozzle to the etching liquid toimprove remarkably.

Other processing process of the preferred embodiment of the invention isexplained by referring to embodiment 2. FIGS. 2A to 2D, FIGS. 3A to 3Cand FIG. 4 explain embodiment 2. FIGS. 2A to 2D are process charts ofembodiment 2 showing the process in the case of using the photo resistas mask and semiconductor as processing object. FIGS. 3A to 3D areprocess charts of embodiment 2 showing the process in the case of usingthe coating substance as mask and semiconductor as processing object.And FIG. 4 is an explanatory diagram of etching apparatus of embodiment2 in the case of using semiconductor as processing object.

As an example of fine patterning of processing object 30, the latestprocessing of fine patterning of semiconductor device is explained.

In 2002, generally, the semiconductor is processed more finely than 0.25μm. Accordingly, the size of fine particles of liquid 70 for processingit should be smaller than 0.2 μm. The size of fine particles may besmall enough for the factor determining the size of the object ofprocessing (critical dimension). If the required processing precision islarge, the size of a corresponding particle may be selected from sizessmaller than the required processing precision. In embodiment 2, theetching apparatus includes nozzles 50 for forming fine particles smallerthan 0.2 μm, or supersonic nozzles 51 for forming liquid fine particlesat higher speed. In the invention, the supersonic nozzles spray liquidfine particles at a speed of no less than 1000 km/hour, or morepreferably spray liquid fine particles by accelerating to a speed of noless than 3,000 km/hour.

Referring to FIG. 2, the semiconductor substrate to be processed isexplained. As an example of semiconductor substrate, a silicon wafer 90forming a thin film 100 of a substance necessary for forming asemiconductor element thereon is used. The semiconductor substrate to beprocessed is silicon substrate, or silicon substrate forming siliconoxide film, silicon nitride film, oxide film of rare earth elements, ormetal film of aluminum or copper, thereon.

Although there are various liquid for etching the thin film 100 ofprocessing object material, a solvent suitable for the material of thesemiconductor substrate to be processed is selected and used.

The degree of vacuum of vacuum chamber 10 is kept higher than about 1E-3Torr, and the liquid 70 is sprayed from the nozzles 50 at a speed of noless than about 1000 km/hour. When the sprayed liquid reaches and wetsthe processing object surface 31, it is etched at the same time.Depending on a relation between processing object surface 31 and liquid70, a surface active agent is used for the liquid permeating into allparts of the processing object surface 31, and for obtaining ahomogeneous etching effect. If wetting of liquid 70 on the processingobject surface 31 is poor, by spraying the surface active agent to theprocessing object surface, the liquid 70 is distributed in all parts ofthe processing object surface 31, so that uniform etching is attained.

For example, if the liquid 70 reaches the processing object at a highspeed exceeding about 10,000 km/hour, part of liquid components may betransformed into plasma by receiving high energy. The generated plasmaactivates the processing object surface, and may further accelerate theetching speed.

When manufacturing a semiconductor device, it may be required to processin a very fine size of 0.1 μm smaller than 0.25 μm. In such a case, asshown in FIG. 2B, a photo resist 110 is formed on the thin film 100,using it as mask, it may be processed in desired pattern and size byusing the so-called lithography. At this time, in order to provide thephoto resist with corrosion resistance to withstand liquid phaseetching, it is preferred to process the surface of photo resist 110preliminarily by plasma 120 as shown in FIG. 2B.

By plasma processing of the surface of the photo resist composed oforganic materials, polymerization reaction of organic materials takesplace on the surface. By this reaction, cross linking of organicmaterials on the surface is promoted, so that an anticorrosive photoresist 111 obtained as shown in FIG. 2C. An appropriate plasma 120 maybe determined in consideration of: plasma of rare gases; interactionwith substance for composing the photo resist 110; interaction withetching liquid 70 such as solvents, acid or alkali to be used.

Depending on the combination of etching liquid 70 such as solvents, acidor alkali to be used, sufficient corrosion resistance may not beachieved in the photo resist 110 mainly composed of organic materials.

In such a case, as shown in FIG. 3, a coating substance 130 made ofmaterial having enough corrosion resistance is applied on the surface ofthe processing object 100, and liquid phase etching is executed by usingthe coating substance 130 as mask. In embodiment 2, the processingobject corresponds to the thin film 100 formed on the surface of siliconsubstrate 90.

At first, using the photo resist 110 as mask, the coating substance 130is etched by using etching liquid 70, such as solvent, acid or alkali,capable of etching the coating substance 130.

Further, using the patterned coating substance 131 as mask, as shown inFIG. 4, in the vacuum chamber 10, the processing object 100 is etched inliquid phase and processed as desired by spraying the solvent and acidicor alkaline etching liquid 70 for etching the processing object 100 fromthe supersonic nozzles 51. The vacuum degree in the vacuum chamber 10 iskept at degree of vacuum higher than 1E-3 Torr (that is, lowerpressure), and the liquid 70 is sprayed from nozzles 51 at a speed ofhigher than 1,000 km/hour. The degree of vacuum is thus maintained inorder to prevent generation of impulse waves or the like by surpassingthe sonic speed at the time of jet injection of the chemically reactiveliquid.

By the method explained above, the semiconductor substrate or other thinfilm to be processed can be processed very finely according to the maskpattern.

Other processing process of the preferred embodiment of the invention isexplained below by referring to embodiment 3. In manufacture ofsemiconductor device in which precision processing is required, overhangof etching groove or forming of taper may cause to worsen the processingprecision. Hence, there is a strong demand for an etching method ofdigging groove in the vertical direction from the surface of flat solidbody.

Embodiment 3, by referring to FIG. 5 and FIG. 6, explains an etchingmethod of digging groove in the vertical direction by making use ofelectric field or magnetic field at the time of etching process.

FIG. 5 is an explanatory diagram of etching apparatus for acceleratingthe liquid 70 by applying an electric field to the processing object inembodiment 3 of the invention, and FIG. 6 is an explanatory diagram ofetching apparatus for accelerating the liquid 70 in rotating directionby applying a magnetic field to the vacuum chamber in embodiment 3 ofthe invention.

As shown in FIG. 5, a charging mechanism 140 is provided at the outletor near the outlet of the nozzles 50, and an electric charge is appliedto the ejecting pulverized liquid (that is, liquid particles) 70. Bymaking use of this electric charge, the ejecting pulverized liquid 70 isprovided with freedom in directivity. For this purpose, a voltageapplication mechanism 150 is provided for applying a voltage to thestage holding the semiconductor solid.

The liquid 70 sprayed out from the nozzles 50 is first provided with anelectric charge by the charging mechanism 140, and is accelerated by thevoltage application mechanism 150 and reaches the processing object 30.The applicable voltage is limited by electric discharge or leak varyingwith the structure of the apparatus or electrical characteristic of theliquid to be used. This problem will be further discussed in embodiment5. By applying the voltage intermittently by combining with a system ofpromoting vaporization of the liquid used in the etching, effects ofcurrent leak or the like may be prevented.

Further, as shown in FIG. 6, by using a magnetic field applicationmechanism 160 for applying a magnetic field, the liquid 71 can beaccelerated in the rotating direction, and the motion trajectory can bevaried, and the direction can be controlled freely. Reference numeral 71refers to the liquid rotated in its trajectory.

Another processing process of the preferred embodiment of the inventionis explained below by referring to embodiment 4. Only one nozzle 50 forinjecting liquid may be used in etching process, but when the processingobject such as a solid has a certain area, if only one nozzle is usedthen, the incident angle to the surface of the pulverized liquidparticles varies depending on the location of the processing. This isthe same phenomenon as a flat surface illuminated by a spot light sourcevaries in luminance depending on the location. Therefore, to processuniformly on the entire surface of the processing object, it iseffective to use plural nozzles. In embodiment 4, a case of using theplural nozzles is explained.

FIG. 7 shows an etching apparatus in embodiment 4 of the invention, inwhich nozzles are provided at every individual semiconductor chip. FIG.8 shows an etching apparatus having numerous fine nozzles by making useof MEMS in embodiment 4 of the invention.

For example, in the manufacturing process of silicon semiconductor,plural chips 170 are formed at intervals of about 1 cm. As shown in FIG.7, nozzles 50 are installed immediately above the individual chips 170,and the angle variation of liquid 70 may be minimized. Besides, byinstalling the plural nozzles in every chip, effects of angle changesmay be minimized.

Further, as shown in FIG. 8, for example, by using micro nozzles 52making use of MEMS or micro machining, nozzles may be disposed atintervals of several microns. At this time, etching may be carried outusing nozzles densely installed in an area corresponding to the entiresurface of the processing object. Or by installing nozzles in a specificarea, and by moving the nozzles or the processing object, the entiresurface of the processing object may be etched. In FIG. 8, each nozzleis shown in magnified view for the sake of explanation.

A further processing process of the preferred embodiment of theinvention is explained below by referring to embodiment 5. Depending onthe characteristic of the etching liquid, such as solvent, acid oralkali, used in liquid phase etching, the time of vaporization of theliquid used in the etching in the vacuum chamber 10 varies.

When the vaporization speed is sufficiently fast, the sprayed liquid issoon vaporized after a specified etching time and there is no problem.If the vaporization speed is slow, the liquid remains after necessaryetching time, which may lead to etching defects. Accordingly, when thevaporization speed is slow, it is required to prevent excessive supplyof liquid by controlling the spraying amount of the etching liquid. Tosolve this problem, the liquid feed device 60 includes an intermittentspray circuit or intermittent spray device (not shown), and the liquidis sprayed from the nozzles intermittently, and it is preferred to set anecessary time interval for allowing the etching liquid to be evaporatedafter being sprayed out.

In the foregoing preferred embodiment, it is desired to spray thechemically reactive liquid at super high speed, but if not so high, thespeed may be enough as far as part or most of liquid components can betransformed into plasma.

INDUSTRIAL APPLICABILITY

As explained herein, the invention presents a liquid phase etchingmethod capable of spraying an etching liquid to the processing object ata high speed, and is intended to enhance the etching speed substantiallywhile maintaining anisotropy or other fine patterning performance of dryetching.

1. A liquid phase etching apparatus comprising: a vacuum chamber; and anozzle mechanism provided in the vacuum chamber for spraying a chemicalreactive liquid to a processing object in vacuum atmosphere, wherein atleast the nozzle mechanism is protected by anticorrosive treatment, theanticorrosive treatment is a process of forming a thin film of substancehaving corrosion resistance to the liquid in the exposed part of thenozzle mechanism, and the treatment is a surface treatment by usingplasma.
 2. The liquid phase etching apparatus of claim 1, furthercomprising: a stage for holding the processing object, a chargingmechanism provided at the exit of the nozzle mechanism, and a voltageapplication mechanism for applying a voltage to the stage, wherein thecharging mechanism applies an electric charge to particles of thesprayed liquid, and the voltage application mechanism can accelerate thecharged particles of the liquid.
 3. The liquid phase etching apparatusof claim 1, further comprising a magnetic field application mechanism,wherein the magnetic field application mechanism controls the trajectoryof liquid particles.
 4. The liquid phase etching apparatus of claim 1,further comprising a liquid feed device, wherein the liquid feed devicefeeds the liquid continuously or intermittently to the nozzle mechanism.5. The liquid phase etching apparatus of claim 1, further comprising asurface active agent feed mechanism, wherein the surface active agentfeed mechanism includes: a spraying section for spraying the surfaceactive agent to the processing object, and a feed device for feeding thesurface active agent to the spraying section.
 6. The liquid phaseetching apparatus of claim 1, wherein the vacuum atmosphere has higherdegree of vacuum than 1E-3 Torr.